Roles of water vapor sources and transport in the intraseasonal and interannual variation in the peak monsoon rainfall over East China

ERA-Interim reanalysis data from 1979 to 2017 are utilized to analyze the intraseasonal and interannual variabilities in the moisture transport associated with the summer rainfall over East China. Three key issues of moisture sources for East China summer precipitation are discussed in this study: the identification of the primary moisture sources of summer precipitation, determination of their individual contributions to the intraseasonal variation in summer precipitation, and determination of the extent to which each source affects the interannual variation in precipitation during the peak monsoon rainfall period (PMRP). Through the Lagrangian method, the water vapor is divided into six sources, namely, the land area source, East China source (EC source, except for the target region), Indian Ocean source (IO source), Pacific Ocean source, South China Sea source, and regional evapotranspiration sources. This study proposes that the rainfall over South China during the PMRP is mainly influenced by the IO source water vapor transport (52.4%). For the middle and lower Yangtze River valley, the rainfall contribution from southwesterly moisture transport accounts for approximately 50% of the total rainfall during the PMRP and determines the intraseasonal and interannual variation in the summer rainfall. The water vapor from terrestrial evaporation, which includes EC source water vapor (38.9%) and North China (NC) source water vapor (21.8%), is the most important moisture source for rainfall over NC during the PMRP.